The invention relates to a system of propulsion for a ship comprising a front and a rear propelling engine the propulsion powers of which can be coupled to an output shaft via a gear system, said output shaft being passed through below the rear propelling engine.
Already known are propulsion systems for ships in which two propellers can be driven by twoxe2x80x94equal or differentxe2x80x94propelling engines. Depending on the power requirement propulsion systems for ships, having several prime movers, permit driving only one or more prime movers. A lower fuel consumption is hereby achieved in the area of a part load. Besides, the reliability of operation increases, since even in case of failure of individual propelling engines, the ship remains capable of maneuvering.
Particularly in heavy-duty ships, such as catamaran ferries which can attain very high speeds, special requirements are placed on the propulsion system. They must have light weight and claim only narrow installation space because of the narrow hulls. Between conventionally used, high-speed diesel engines and their ship output shaft, which drives a propeller or other output element of the ship, only relatively small ratios are needed in the gear between the input shafts and the output shaft due to the high speeds of the ship under certain propelling variants.
Large ships are usually optimized especially to a provided use profile. Different propulsion plans with stationery or adjustable propellers with so-called waterjet propulsions are used here. Accordingly different demands are placed on the ship propulsion systems and the ship gear mechanism thereof which demands as a rule require, expensive special solutions.
By prior use has become known, a ship gear system in which two propelling engines are disposed consecutively in longitudinal direction and their propulsion powers can be coupled to a ship output shaft, via a gear mechanism, situated between the propelling engines, the ship output shaft being passed through below the rear propelling engine. Determined by the kind of construction, the input shaft of the rear propelling engine has only a small axial distance from the output shaft. In order that the ship output shaft can be passed through below, the rear propelling engine, in this gear system the rear propelling engine is coupled to the gear mechanism with large axial distance by means of a suitable cardan shaft. The required large axial installation space made necessary by a large engine space is disadvantageous here. But large continuous spaces, uninterrupted by a partition, are unfavorable for safety reasons. In addition, the rear propelling engine is installed, tilted in relation to the other components of the propulsion system. By the cardan shaft that extends inclined, undesirable vibrations can be excited in the drive chain. Both propelling engines also have, relative to each other, a horizontal offset so that the propulsion system is altogether built wider than were actually needed, based on the measurements of the individual propelling engines.
EP 0 509 712 A1 has finally disclosed a ship propulsion system, having a front and a gear propelling engine, the propulsion powers of which can be coupled to a ship output shaft, via a gear system, consisting of two interconnected gears. Both the input shafts and the output shaft of said gear system are only vertically offset in relation to each other so that both propelling engines can be situated in the ship hull without horizontal offset thus saving space. The vertical axial distance between the rear input shaft and the output shaft is large enough for a cardan shaft to be omitted between the rear propelling engine and the gear system. This ship propulsion system, of course, has some disadvantages. The use of two interconnected gears results in a higher total weight and the need of a larger axial installation space. In the fitting in the ship, great expenditure in assembly and alignment is required in order to prevent mutual restraints. The gear system also has a very large number of parts. In the arrangement shown with opposite output sides of the propelling engines, it is also required to use propelling engines having opposite directions of rotation.
Therefore, the problem on which this invention is based is to provide a ship propulsion system which is of simpler construction, needs less installation space, has a light weight despite a relatively small ratio and allows the utilization of propelling engines that rotate in the same direction. The ship propulsion system must also be adaptable at low expense to the requirements established by different propulsion plans.
The inventive propulsion system for ships has one gear mechanism in which the front input shaft is situated upon a first axis of rotation, the rear input shaft upon a second axis of rotation and the output shaft upon a third axis of rotation. The second axis of rotation extends vertically here above the first axis of rotation and the first axis of rotation vertically above the third axis of rotation. One input gear placed upon the rear input shaft is permanently meshed with an intermediate gear placed upon the first axis of rotation of the front input shaft and an output gear placed upon the gear output shaft is simultaneously engaged with an intermediate gear placed upon the first axis of rotation. Hereby results a large vertical axial distance between the rear input shaft and the gear output shaft.
With a relatively small ratio of 2:1, for example, between the input and the output shaft, there can also be used gear wheels of smaller diameter, since the axial distance between the axes of rotation is added. The point of gravity of the front propelling engine is lower in the ship hull than in the rear propelling engine, which is favorable with regard to a stablest possible position of the ship.
Sparing place both propelling engines can be disposed without horizontal axial distance when the second axis of rotation extends without horizontal offset exactly in vertical manner over the first axis of rotation. The maximum axial distance between the rear input shaft and the gear output shaft is obtained when the third axis of rotation extends without horizontal offset in exactly vertical manner below the first and the second axes of rotation.
In a preferred embodiment, the first, the second and the third axes of rotation extend parallel to each other. Only cylindrical spur gears are necessary here in the gear mechanism and both propelling engines can be installed parallel to each other. Alternatively a so-called down-angle arrangement is also possible in which the gear output shaft extends downwardly inclined. The gear output step is, in this case, a bevel gear step. The advantage of such an arrangement consists in that both propelling engines can be installed horizontally in the ship while the ship output shaft can be passed through the bottom of the hull with an angle of inclination.
Together with the inventive ship gear system and the developments thereof, protection is claimed also for a ship gear mechanism of such a ship gear system.